The /30 subnet
A /30 subnet uses the mask 255.255.255.252 and holds 4 addresses, 2 of them usable.
A /30 gives you four addresses and two usable hosts, with the mask 255.255.255.252. It is the classic size for a point-to-point link between two routers when RFC 3021 /31 support is not available.
The four addresses break down as one network, two hosts, and one broadcast. That two-host budget is exactly what a WAN link or a firewall-to-router handoff needs, which is why /30 shows up constantly in enterprise routing.
Below you can see the exact network, broadcast, and host range for any /30 you enter, calculated instantly in your browser.
Calculate a /30 network
Accepts CIDR (192.0.2.0/24), IP + mask (192.0.2.0 255.255.255.0), or a bare IP (defaults to /24).
11000000.00000000.00000010.0000000011111111.11111111.11111111.11111100Example: 192.0.2.0/30
Taking 192.0.2.0/30 as a worked example, the block breaks down like this:
| Network address | 192.0.2.0 |
|---|---|
| Usable range | 192.0.2.1 - 192.0.2.2 |
| Broadcast address | 192.0.2.3 |
| Total addresses | 4 |
| Usable hosts | 2 |
| Size | 1/64 of a class C block |
Frequently asked questions
What is the subnet mask for a /30?
A /30 uses the subnet mask 255.255.255.252. Its wildcard mask, used in access lists, is 0.0.0.3.
How many hosts are in a /30 subnet?
A /30 has 4 total addresses and 2 usable hosts (the total minus the network and broadcast addresses, except for /31 and /32).
What is a /30 used for?
Point-to-point link (2 usable). It is equivalent to 1/64 of a class C block.
How do I calculate a /30 network?
Set the host bits to zero for the network address and to one for the broadcast address. The calculator on this page does it for any /30 block you enter.